The present invention relates to the design and manufacture of automotive substrates or other ceramic honeycombs exhibiting substantial improvements in isostatic strength over conventional honeycomb while maintaining or even increasing the thermal shock resistance of the parts. The invention is particularly valuable as applied to thin-wall and ultra thin-wall automotive substrates wherein higher isostatic strengths are important for purposes such as packaging and extended service life.
Various methods have been proposed for improving the isostatic strength of thin-wall and ultra thin-wall ceramic honeycomb substrates, i.e., honeycombs having cellular matrix portions formed of ceramic walls in the range of about 20-125 μm in thickness. Some of these methods include increasing the cell density over regions of the cellular matrix portion near the periphery of the parts, thickening the cell walls or webs at the periphery of the cellular matrix portion, thickening web intersections at the periphery by means such as corner rounding or filleting, and thickening or strengthening the skins through the use of strength enhancing coatings or additives. U.S. Patents and patent applications Nos. U.S. Pat. No. 4,233,351-A1, U.S. Pat. No. 6,159,431-B1, U.S. 2002-0192426-A1 and U.S. Pat. No. 5,714,228-B1 are representative.
While these gradual peripheral strengthening approaches are often helpful to increase isostatic strength, they almost invariably result in a reduction in the ability of the thus-modified honeycombs to resist damage from thermal shock. In addition, the web thickening and corner filleting approaches previously proposed for matrix strengthening necessarily reduce the open cross-sections of the honeycombs, resulting in an increased exhaust gas pressure drop across catalytic reactors containing such honeycombs when in use for the treatment of flowing combustion engine exhaust gases.